Right whales are headed out of Georgia waters and back north after a calving season that produced 20 of the highly endangered large whales.

An aerial survey team documented the last of the new babies March 18 just off Tybee Island. It was swimming with its mother, a 10-year-old whale named Harmony, and appeared to be about a month old. Harmony has given birth once before.

“Twenty calves is slightly above average, so that’s encouraging,” said Clay George, a biologist with the Georgia Department of Natural Resources. “In addition to mom/calf pairs, the survey teams documented approximately 120 other individual right whales in the Southeast this winter.”

Tricia Naessig, right whale survey coordinator with the EcoHealth Alliance, on Wednesday bumped that number up to 140 whales, not including the new calves. The number of calves born in the last two decades has varied widely by year, Naessig said. Just one calf was born in 2000, but the next year that number was up to 31.

EcoHealth Alliance, formerly called Wildlife Trust, is a nonprofit that along with state and federal agencies monitors and catalogs right whales.

About 450-470 North Atlantic right whales are believed to exist, Naessig said. Their population was decimated by whalers in the 1800s when they were the “right” whale to hunt because they are big, slow and float when killed. Considered an urban whale because they swim near the highly populated U.S. East Coast, right whales feed in the waters off New England in the summer, eating tiny crustaceans they filter through their baleen plates. In winter, pregnant females and some juveniles head south to their only known calving area, off the Georgia and Florida coasts. They don’t feed while they’re in these waters.

Right whales seemed to head a little farther south than usual this year, presumably because of colder water temperatures, George said.

Aerial surveys also produced four sightings of great white sharks, each about seven or eight miles off Jekyll and Cumberland islands. Carolyn Belcher, a DNR biologist who studies sharks, said it’s theorized that the sharks follow pregnant right whales to the calving grounds.

“It’s like lions and other big predators; they go for the weak, the sick and the young,” she said. In fact, over the last decade bite marks on the carcasses of right whales found in the Southeast have been identified as coming from great whites.

It’s unclear if great white sharks are more abundant off Georgia than they were in the past, George said. It’s possible that the advent of digital photography has just made it easier to identify the rare sharks during aerial surveys. Belcher said they prefer cold, deep water.

“To my knowledge there have not been any close to the beach line where you’d worry about them encountering somebody swimming,” she said.

Modern threats to right whales include collisions with ships and entanglement in fishing gear. The three aerial survey teams that covered the coast from the southern North Carolina border to south of St. Augustine, Fla., documented five newly discovered entangled whales this season. Biologists, including George and DNR colleague Mark Dodd, were able to sedate one of those whales and remove fishing gear from it, but the young female was subsequently found dead. It was only the second time a whale or dolphin was sedated in the wild, the first time having been in 2009, with largely the same team of biologists. Of the other entangled whales seen in the Southeast this season, three haven’t been seen again and one, a new mother, “looked fine the last time she was sighted,” George said.

Naessig said one unusual sighting this season was also a sad one. On Christmas Day a calf was seen swimming by itself.

“The assumption was the calf would not survive,” she said. “It’s not something we see often at all. We’re not sure who the mother was or what were the circumstances. It could be that something happened to the mother. Or there is the possibility the mother abandoned the calf. That does happen in the wild.”

George and his team got a tissue sample of skin and blubber from the calf. That sample will be used to try to make a genetic match and identify its mother, a possibility because 60 percent of the right whales that have been catalogued by photographs are also genetically catalogued with tissue samples.

“There’s a good chance we can connect them,” Naessig said.

In their ongoing research, DNR biologists sampled 12 calves and 10 other whales just this season.